'''Progressive retinal atrophy (PRA)''' is a group of [[Genetics|genetic]] diseases seen in certain breeds of [[dog]]s and, more rarely, cats. It is characterized by the bilateral degeneration of the [[retina]], causing progressive vision loss culminating in blindness. The condition in nearly all breeds is inherited as an [[Recessive gene|autosomal recessive]] trait, with the exception of the [[Siberian Husky]] (inherited as an [[Sex linkage|X chromosome linked]] trait) and the [[Bullmastiff]] (inherited as an [[autosomal dominant]] trait).<ref name="Merck">{{cite web |title=Inherited Retinopathies |work=The Merck Veterinary Manual |date=2006 |url=http://www.merckvetmanual.com/mvm/index.jsp?cfile=htm/bc/30114.htm |accessdate=2007-03-10}}</ref> There is no treatment. PRA is similar to [[retinitis pigmentosa]] in humans.<ref name="Petersen">{{cite web |last=Petersen-Jones |first=Simon M. |title=Progressive Retinal Atrophy: An Overview |work=Proceedings of the 28th World Congress of the World Small Animal Veterinary Association |date=2003 |url=http://www.vin.com/proceedings/Proceedings.plx?CID=WSAVA2003&PID=6687&O=Generic |accessdate=2007-03-10}}</ref>

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==Diagnosis==

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Progressive vision loss in any dog in the absence of [[canine glaucoma]] or [[cataract]]s can be an indication of PRA. It usually starts with decreased vision at night, or [[nyctalopia]]. Other symptoms include dilated [[pupil]]s and decreased [[pupillary light reflex]]. [[Fundoscopy]] to examine the retina will show shrinking of the blood vessels, decreased pigmentation of the nontapetal [[fundus (eye)|fundus]], increased reflection from the [[tapetum lucidum|tapetum]] due to thinning of the retina, and later in the disease a darkened, atrophied [[optic disc]]. Secondary cataract formation in the posterior portion of the [[lens (anatomy)|lens]] can occur late in the disease. In these cases diagnosis of PRA may require [[electroretinography]] (ERG). For many breeds there are specific [[genetic testing|genetic tests]] of blood or [[buccal mucosa]] for PRA.<ref name=Merck/>

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| Ilse Valtierra

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| ivaltier@lcg.unam.mx

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==Types of PRA==

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'''Generalized PRA''' is the most common type and causes [[atrophy]] of all the neural retinal structures. '''Central progressive retinal atrophy''' (CPRA) is a different disease from PRA involving the [[retinal pigment epithelium]] (RPE), and is also known as '''retinal pigment epithelial dystrophy''' (RPED).

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| Amhed Vargas Velazquez

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Generalized PRA can be divided into either dysplastic disease, where the [[cell (biology)|cell]]s develop abnormally, and degenerative, where the cells develop normally but then undergo a damaging change. PRA can be further divided into affecting either [[rod cell|rod]] or [[cone cell]]s. Rod cells detect shape and motion, and function in dim light. Cone cells detect color and definition, and function in bright light.

*[[Akita Inu|Akita]] - Symptoms at one to three years old and blindness at three to five years old.

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| wgarcia@lcg.unam.mx

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*Miniature longhaired [[Dachshund]] - Symptoms at six months old.

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*[[Papillon (dog)|Papillon]] - Slowly progressive with blindness at seven to eight years old.

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*[[Tibetan Spaniel]] - Symptoms at three to five years old.

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| Augusto Berrocal

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*[[Tibetan Terrier]] - Symptoms at less than one year old, often blind by two years old, and cataract formation by four years old.

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| nberro@lcg.unam.mx

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*[[Samoyed (dog)|Samoyed]] - Symptoms by three to five years old.

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| Marco Antonio Ortiz Sanchez

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===Rod-cone dysplasia===

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This type of PRA has an early onset of severe vision loss. It is caused by a defect in the gene for cGMP-[[phosphodiesterase]], which leads to retinal levels of [[cyclic guanosine monophosphate]] ten times normal.<ref name=Bedford>{{cite web | last = Bedford | first = Peter | title = Hereditary Retinal Diseases | work = Proceedings of the 31st World Congress of the World Small Animal Veterinary Association | date = 2006 | url = http://www.ivis.org/proceedings/wsava/2006/lecture21/Bedford2.pdf?LA=1 | format=PDF | accessdate = 2007-03-10 }}</ref>

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====Rod-cone dysplasia type 1====

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*[[Irish Setter]] - Rod cell response is nearly absent. Night blindness by six to eight weeks old, often blind by one year old.<ref name=Gelatt_1999/>

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| Daniela Garcia Soriano

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*[[Sloughi]]<ref name=Petersen/> - A DNA test can identify whether Sloughis have the mutated recessive gene. This has enabled breeders to breed away from PRA, and the disease is now rare in the breed.

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| dgarcia@lcg.unam.mx

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====Rod-cone dysplasia type 2====

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*[[Collie]] - Rod cell response is nearly absent. Night blindness by six weeks old, blind by one to two years old.<ref name=Gelatt_1999/>

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| Laura Gomez Romero

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| lgomez@lcg.unam.mx

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====Rod-cone dysplasia type 3====

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*[[Cardigan Welsh Corgi]]<ref name=Petersen/>

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| Hector Fco. Medina A.

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===Rod dysplasia===

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*[[Norwegian Elkhound]] - Characterized by dysplasia of the rod cell unit and subsequent degeneration of the cone cell unit. Rod cell response is nearly absent. Night blindness by six months old, blind by three to five years old. Rod dysplasia has now been bred out of this breed.<ref name=Gelatt_1999/>

*[[Alaskan Malamute]] - Temporary loss of vision in daylight ([[hemeralopia]]) at eight to ten weeks old. There is a purely rod cell retina by four years old.<ref name=Gelatt_1999/>

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| jzepeda@lcg.unam.mx

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| 59-59-57-45-41

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===Progressive rod-cone degeneration (PRCD)===

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This is a disease with normal rod and cone cell development but late onset degeneration of the rod cells that progresses to the cone cells. It is inherited as an autosomal recessive trait and has been linked to the ninth canine [[chromosome]].<ref name=Petersen/>

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| Jose Alfredo Samaniego Castruita

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*[[Poodle]] - Night blindness by three to five years old, blind by five to seven years old.

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| jsamanie@lcg.unam.mx

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*[[English Cocker Spaniel]] - Occurs late in life, usually at four to eight years old.

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*[[American Cocker Spaniel]] - Night blindness by three to five years old, blind one to two years later.

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*[[Labrador Retriever]] - Night blindness by four to six years old, blind at six to eight years old.

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| Jose Reyes Lopez

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*[[Portuguese Water Dog]]<ref name=Gelatt_1999/>

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| jreyes@lcg.unam.mx

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*[[Chesapeake Bay Retriever]]

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*[[Australian Cattle Dog]]

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*[[Nova Scotia Duck Tolling Retriever]]<ref name=Petersen/>

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| Abraham Avelar

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===X-linked PRA===

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This condition is linked to the [[X chromosome]].

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*[[Siberian Husky]] - Night blindness by two to four years old.<ref name=Gelatt_1999/>

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*Samoyed - More severe disease than the Husky.<ref name=Petersen/>

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===Dominant PRA===

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*[[Bullmastiff]] - Inherited as an autosomal dominant trait due to a mutation in the gene for [[rhodopsin]].<ref name=Petersen/>

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===Feline PRA===

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*[[Abyssinian (cat)|Abyssinian]] - Two forms exist. One is inherited as an autosomal dominant trait and has an early age onset. The other is inherited as an autosomal recessive trait and has a middle age onset.<ref name=Petersen/>

CPRA is also known as '''retinal pigment epithelial dystrophy''' (RPED). The cause of this condition is the loss of the retinal pigment epithelium's ability to effectively process the [[photoreceptor cell|photoreceptor]] outer segment (POS) and subsequent accumulation of POS material in the RPE and loss of function. The loss of function of the RPE leads to photoreceptor degeneration.<ref name=Bedford/> [[Vitamin E]] deficiency may play a role in the development of CPRA.<ref>{{cite journal |author=Davidson M, Geoly F, Gilger B, McLellan G, Whitley W |title=Retinal degeneration associated with vitamin E deficiency in hunting dogs |journal=J Am Vet Med Assoc |volume=213 |issue=5 |pages=645–51 |year=1998 |pmid=9731258}}</ref> It is characterized by accumulation of pigment spots in the retina surrounded by retinal atrophy and a mottled appearance of the pigmented nontapetal fundus. The pigmented spots eventually coalesce and fade as the atrophy of the retina increases. It is an inherited condition (in the Labrador Retriever it is inherited as an autosomal dominant trait with variable [[penetrance]]).<ref name=Merck/> CPRA occurs in older dogs. Peripheral vision is retained for a long time. Vision is better in low light and better for moving or distant objects. Not all affected dogs go blind. Secondary cataracts are common.

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====Commonly affected breeds====

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*[[Labrador Retriever]]

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*[[Golden Retriever]]

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*[[Border Collie]]

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*[[Collie]]

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*[[Shetland Sheepdog]]

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*[[English Cocker Spaniel]]

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*[[English Springer Spaniel]]

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*[[Chesapeake Bay Retriever]]

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*[[Cavalier King Charles Spaniel]]

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*[[Briard]] - has an especially high frequency.<ref name=Gelatt_1999/>

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*It can also, but very rarely, be found in the [[Papillon (dog)|Papillon]].{{Fact|date=February 2007}}

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It can also be found in the poodle varieties

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===Hereditary retinal dysplasia===

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There is another retinal disease in Briards known as hereditary retinal dysplasia. These dogs are night blind from birth, and day vision varies. Puppies affected often have [[pathologic nystagmus|nystagmus]]. It is also known as '''lipid retinopathy'''.<ref name=Gelatt_1999/>

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==See also==

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*[[Sudden acquired retinal degeneration]]

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==References==

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<div class="references-small"> <references/> </div>

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[[Category:Dog diseases]]

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[[Category:Ophthalmology]]

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[[de:Progressive Retinaatrophie]]

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Diagnosis

Progressive vision loss in any dog in the absence of canine glaucoma or cataracts can be an indication of PRA. It usually starts with decreased vision at night, or nyctalopia. Other symptoms include dilated pupils and decreased pupillary light reflex. Fundoscopy to examine the retina will show shrinking of the blood vessels, decreased pigmentation of the nontapetal fundus, increased reflection from the tapetum due to thinning of the retina, and later in the disease a darkened, atrophied optic disc. Secondary cataract formation in the posterior portion of the lens can occur late in the disease. In these cases diagnosis of PRA may require electroretinography (ERG). For many breeds there are specific genetic tests of blood or buccal mucosa for PRA.<ref name=Merck/>

Types of PRA

Generalized PRA is the most common type and causes atrophy of all the neural retinal structures. Central progressive retinal atrophy (CPRA) is a different disease from PRA involving the retinal pigment epithelium (RPE), and is also known as retinal pigment epithelial dystrophy (RPED).

Generalized PRA can be divided into either dysplastic disease, where the cells develop abnormally, and degenerative, where the cells develop normally but then undergo a damaging change. PRA can be further divided into affecting either rod or cone cells. Rod cells detect shape and motion, and function in dim light. Cone cells detect color and definition, and function in bright light.

Rod-cone dysplasia type 2

Rod-cone dysplasia type 3

Rod dysplasia

Norwegian Elkhound - Characterized by dysplasia of the rod cell unit and subsequent degeneration of the cone cell unit. Rod cell response is nearly absent. Night blindness by six months old, blind by three to five years old. Rod dysplasia has now been bred out of this breed.<ref name=Gelatt_1999/>

Cone degeneration

Alaskan Malamute - Temporary loss of vision in daylight (hemeralopia) at eight to ten weeks old. There is a purely rod cell retina by four years old.<ref name=Gelatt_1999/>

Progressive rod-cone degeneration (PRCD)

This is a disease with normal rod and cone cell development but late onset degeneration of the rod cells that progresses to the cone cells. It is inherited as an autosomal recessive trait and has been linked to the ninth canine chromosome.<ref name=Petersen/>

Poodle - Night blindness by three to five years old, blind by five to seven years old.

X-linked PRA

Siberian Husky - Night blindness by two to four years old.<ref name=Gelatt_1999/>

Samoyed - More severe disease than the Husky.<ref name=Petersen/>

Dominant PRA

Bullmastiff - Inherited as an autosomal dominant trait due to a mutation in the gene for rhodopsin.<ref name=Petersen/>

Feline PRA

Abyssinian - Two forms exist. One is inherited as an autosomal dominant trait and has an early age onset. The other is inherited as an autosomal recessive trait and has a middle age onset.<ref name=Petersen/>

It has been requested that this page be removed with restriction endonucleases.Other articles for deletion are listed here.

</ref> Despite belief among breeders to the contrary, there is apparently no link between coat color in Persians and the development of PRA.<ref>

It has been requested that this page be removed with restriction endonucleases.Other articles for deletion are listed here.

</ref>

Central progressive retinal atrophy (CPRA)

CPRA is also known as retinal pigment epithelial dystrophy (RPED). The cause of this condition is the loss of the retinal pigment epithelium's ability to effectively process the photoreceptor outer segment (POS) and subsequent accumulation of POS material in the RPE and loss of function. The loss of function of the RPE leads to photoreceptor degeneration.<ref name=Bedford/> Vitamin E deficiency may play a role in the development of CPRA.<ref>

It has been requested that this page be removed with restriction endonucleases.Other articles for deletion are listed here.

</ref> It is characterized by accumulation of pigment spots in the retina surrounded by retinal atrophy and a mottled appearance of the pigmented nontapetal fundus. The pigmented spots eventually coalesce and fade as the atrophy of the retina increases. It is an inherited condition (in the Labrador Retriever it is inherited as an autosomal dominant trait with variable penetrance).<ref name=Merck/> CPRA occurs in older dogs. Peripheral vision is retained for a long time. Vision is better in low light and better for moving or distant objects. Not all affected dogs go blind. Secondary cataracts are common.

Hereditary retinal dysplasia

There is another retinal disease in Briards known as hereditary retinal dysplasia. These dogs are night blind from birth, and day vision varies. Puppies affected often have nystagmus. It is also known as lipid retinopathy.<ref name=Gelatt_1999/>